The cancer treatment modality called "hyperthermia" has been used to successfully treat thousands of cancer patients around the world. However, hyperthermia has never achieved its true potential because of technical limitations in steering and focusing the heating pattern. The goal of this project is the solution of some of those problems. To do so, we will build and test an elliptical 24 dipole phased array applicator system (called the Sigma Ellipse). This new RF applicator will be innovative in four respects: l) the applicator will have the capability of varying the longitudinal length of the energy focus; 2) the primary heating pattern will have three dimensional dynamic electronic steering capability; 3) the applicator will have the ability to reduce localized superficial heating without significantly altering the central heating focus; 4) the applicator will have an elliptical shape in order to reduce the amount of bolus water weight supported anteriorly by the patient. These improvements will increase treatment effectiveness and patient tolerance. Included with this project will be: a new multi-channel RF generator with independent phase and amplitude capabilities and a modified external B-field sensing probe system for enhanced treatment monitoring. If this project is successful in achieving the expected improvements, the prototype designs will be refined for manufacturing and for clinical trials. Success in this project would provide the potential for a major improvement in the treatment of cancer throughout the world.